Lockbolt joint and method of making a lockbolt joint

ABSTRACT

A lockbolt collar configured to reduce the longitudinal tension in a lockbolt which otherwise has the effect of reducing its cross section, and hence the tightness of its fit where it passes through the secured parts, the longitudinal tension being caused by the swaging of the collar onto the lockbolt. An external taper of the collar toward its end adjacent the secured parts commencing at a location intermediate its ends provides a spatial cavity within the swaging die of sufficient size to receive collar material displaced during swaging and thereby significantly reduce the reverse flow of such collar material causing such longitudinal tension in the lockbolt.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 614,774, filed Sept. 19,1975, now abandoned, which in turn is a continuation of application Ser.No. 480,840 filed June 19, 1974, now abandoned, the benefit of thefiling dates of which are hereby claimed under 35 USC 120.

BACKGROUND OF THE INVENTION

This invention relates generally to the lockbolt art, and morespecifically concerns lockbolt collars which are used in combinationwith lockbolts to securely clamp two or more overlapped parts together.

Lockbolts are commonly used where high strength fasteners are required,such as in aircraft fuel tanks and aircraft cabins. Typically, alockbolt collar is provided for use with a lockbolt which, when forcedagainst the typically plate-like members forming the structure (e.g.,fuel tanks or aircraft cabins) over that portion of the lockbolt whichextends through the overlapped members and properly swaged to mate witha lockbolt, provides a reliable, high-strength fastener for thestructure. Such a combination lockbolt and collar is disclosed in U.S.Pat. No. 3,094,017 to Champoux et al. In many such applications, aninterference fit between the plate-like members and the lockbolt isrequired in order to insure the necessary tightness of the joint betweenthe members and the lockbolt. To provide such an interference fit, thelockbolt itself is made slightly larger in diameter than the openings inthe members through which the lockbolt is to fit. The lockbolt is forcedthrough the openings, thereby slightly deforming the material in themembers adjacent the openings to accommodate the lockbolt, and creatingan extremely tight (i.e., fuel tight) interference fit between themembers and the lockbolt. In many applications, it is essential thatsuch an interference fit be created and maintained for proper operationof the structure in which it is used.

It has been discovered, however, that the tightness of the interferencefit between a lockbolt and the members is reduced, and in some caseseliminated, during the process of swaging the collar onto the lockbolt.In many applications, this can lead to the rejection or failure of thestructure in which the interference fit is used. The present inventionis directed to a solution of this reduction in the tightness of theinterference fit caused by the process of swaging.

In accordance with this invention, it has been discovered that the lossof interference fit is caused by a collar material flow phenomenon whichoccurs during the swaging process. After the collar is fitted over thelockbolt, and the swaging die is positioned adjacent the end of thecollar farthest from the overlapped members, swaging begins by forcingthe swaging die against the collar toward the plate members. Duringswaging, some collar material is forced into the annular grooves of theexposed ribs of the lockbolt, resulting in a secured mating of thecollar and the lockbolt. The remainder of the collar material displacedby the swaging die, however, is displaced initially in the generaldirection of the nearest of the secured members, and as swagingcontinues, the accumulating excess of collar material, upon reaching thenearest member, first flows radially inward toward the lockbolt, andthen material adjacent the lockbolt tends to flow longitudinally of thelockbolt away from the secured members.

Typically, during the initial stages of swaging, the lockbolt is grippedby the swaging die and a sufficient longitudinal force is exerted on thelockbolt to securely clamp the two members together between the head ofthe lockbolt and the collar. As deformation of the material begins, thefirst lockbolt groove (i.e., that groove nearest the initially deformedend of the collar) is substantially filled by collar material, which hasthe effect of locking the lockbolt, the collar, and the overlapped partstogether in that spatial position. At this point, the longitudinaltension force exerted on the lockbolt by the swaging die itself ispreferably released, and deformation of the collar is continued. Thelongitudinal tension exerted on the lockbolt solely by the swagingprocess is sufficient to produce the reverse material flow phenomenon,and subsequent elongation of the lockbolt.

In accordance with the above, it is an object of the present inventionto provide a lockbolt which overcomes the adverse effects of the priorart lockbolt collars described above.

More specifically, it is an object of the present invention to provide alockbolt collar, which, when swaged to mate with a lockbolt will notcause a loss of interference fit between the lockbolt and the partswhich are being clamped by the lockbolt and collar combination.

It is another object of the present invention to provide a lockboltcollar, which, when swaged to mate with a lockbolt, will not result inan undesirable elongation and attendant cross-sectional reduction of thelockbolt.

It is a further object of the present invention to provide a lockboltcollar which, when swaged to mate with a lockbolt, results in theaccumulating excess collar material being left in the vicinity of thenear member rather than being forced in a reverse flow back along thelockbolt.

SUMMARY OF THE INVENTION

According to the invention, a lockbolt collar of swageable material,such as an alloy of aluminum in the case of aircraft fabrication, isprovided for use with a lockbolt to clamp together a plurality of partswhich have aligned openings therein so that a ribbed portion of thelockbolt may be passed therethrough. A swaging die having a cavitytherein defined by a cavity wall which opens on one end of the die isused to accomplish the swaging. The collar is generally ring-like inshape, having a central, generally straight axial bore which extendsbetween two opposed ends of the ring-like collar, which permits theribbed portion of the lockbolt to be passed therethrough. The ring-likecollar has a radial thickness which varies along the length thereof, thecollar including a tapered region along its length, in which region thethickness of the collar decreases in the direction of the one opposedend of the collar which is presented adjacent the parts during swaging.The tapered region is so configured and arranged relative to the cavitywall of the swaging die as the swaging die is driven towards the partsover the grooved portion of the lockbolt as to accommodate the swageablematerial displaced in the direction of the one opposed end duringswaging that movement of material away from the parts during swagingtending to excessively tension the lockbolt and loosen itscross-sectional fit in said parts is prevented.

More specifically, the tapered region extends from substantially midwaybetween the ends of the collar to substantially the end thereof abuttedto the secured members and preferably has a uniform taper. In thepreferred embodiment, the uniform taper is substantially within therange of 8 degrees and 18 degrees.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the collar of the present invention in itspreferred form with part of the collar removed to show its crosssection.

FIG. 2 is a side view of a lockbolt which may be used in combinationwith the collar of the present invention.

FIG. 3 is a side view partly in section showing the combination of thelockbolt and the collar assembled with a pair of plate members and aswaging die poised to begin swaging of the collar.

FIG. 4 is a view similar to FIG. 3 with the swaging of the collar at anintermediate stage, showing the partial deformation of the collar whichoccurs at a point during the process of swaging.

FIG. 5 is a view similar to FIG. 4 showing the swaging processcompleted.

FIG. 6 shows the combination of the lockbolt and the collar with a pairof plate members after swaging the collar is completed, the tip of thebolt being removed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-3, the combination of a lockbolt 12 and a collar 14may be preferably used to tightly clamp together overlapped plate-likemembers 16 and 18 in various special purpose structures such as aircraftfuel tanks and cabins. In such applications, it is necessary thatlockbolt 12 and members 16 and 18 mate in an interference fit, in whichthe openings in the members 16 and 18, through which the lockboltextends, are made slightly smaller than the diameter of the lockbolt.The lockbolt is forced through the slightly smaller openings, therebydeforming the member material adjacent the openings, and resulting in anextremely tight (i.e., fuel or air tight) fit between the lockbolt andthe members. To accomplish and maintain the tight clamping of members 16and 18, collar 14 is swaged or deformed onto that portion of thelockbolt 12 which protrudes immediately beyond plate 16. The swagingprocess is accomplished by a specially configured swaging die 20.Swaging die 20 is typically an elongated, rigid block of material inwhich is defined a cavity 47 communicating with one end 49 thereof, thecavity having a substantially constant diameter or bore 48, except for aflared entrance portion 50. The cavity is sufficiently deep to receivethe entire length of the protruding portion of the lockbolt, and thediameter 48 is selected so as to be slightly smaller than the diameterof the collar, so that the collar is deformed when the swaging die isforced in the direction of the plate members.

In operation, swaging die 20 initially forces the collar 14 firmlyagainst plate 16 by gripping the lockbolt and drawing the lockboltoutwardly, thereby compressing the members 16 and 18 between thelockbolt head and the lockbolt collar. As the swaging tool is driven inthe direction of member 16, the initial portion of the collar 14 isdeformed so as to mold it around the first circumferential groove andrib of the lockbolt, which has the effect of locking the collar in thatposition to the lockbolt. At this point, the longitudinal tensionexerted directly on the lockbolt by the swaging die is terminated, andswaging continues with the swaging tool being driven towards member 16,resulting in further deformation of the material and the molding thereofaround the remainder of the ribs and circumferential grooves of thelockbolt, until the end 49 of the swaging die is adjacent the member 16.

In the prior art, this swaging process has caused a slight elongation ofthe lockbolt, on the order of 30/1000 to 40/1000 of an inch for a collarsimilar to that disclosed in U.S. Pat. No. 2,955,505, with consequentreduction of lockbolt diameter where it passes through members 16 and18. Collars of slightly different configuration produce either slightlygreater or slightly lesser resulting lockbolt elongations depending onthe amount of material displaced in the swaging process. In accordancewith the invention, it has been discovered that this elongation andreduction of lockbolt diameter is due to a reverse material flowphenomenon caused by the process of swaging, as explained in detailabove.

Referring now in detail to FIG. 1, showing an illustrative embodiment ofthe invention, collar 14 is shown having a configuration whichsignificantly reduces or eliminates the reverse material flowphenomenon, and substantially eliminates the stretching or elongation ofthe lockbolt and its reduction in diameter. The collar 14 is preferablymade from a high-strength aluminum alloy, although other materials suchas steel, titanium, or monel may also be used. The collar 14 is in thegeneral shape of a ring having a bore or interior diameter 20 of adimension to fit closely over the projecting annular ribs 22 of lockbolt12. At one end of collar 14 is a narrow annular ring 23 which has adiameter slightly greater than any other portion of the collar, theannular ring extending radially outward from but being intergral withthe collar 14. One side 23a of the annular ring is slightly relieved tofacilitate the initial contact between the collar 14 and the interiorwall of the swaging die 20 at the flared entrance 50 thereof. Annularring 23 is known in the art as a clamp-up ring, and due to theadditional amount of material thereby provided in the direction ofswaging, provides a high initial resistance to swaging as compared withthe remainder of the collar. The resistance to swaging of the enlargedportion of the collar formed by the external annular ring, as measuredby the amount of force exerted on the swaging die necessary to initiatedeformation of the collar, is determined by both the external diameterof the annular ring 23 relative to the remainder of the collar, and thelongitudinal dimension or thickness of the annular ring at its base.Increasing either one of these dimensions will increase the forcenecessary for initiation of deformation of the collar.

Located longitudinally adjacent the annular enlargement or ring 23 is acylindrical portion 26 of uniform diameter, the cylindrical portion 26extending to approximately the longitudinal midpoint of collar 14, forreasons to be discussed hereinafter. The diameter of cylindrical portion26 is slightly smaller than the diameter of annular ring 23.

At the other end of the collar is an annular sealing rib 32, whichprojects longitudinally of the collar from the end face 33 thereof.Briefly, the internal periphery of the rib 32 is a continuation of bore20. The outer surface 35 of the rib 32 is a conic surface which tapersfrom the collar end face 33 to a circular (edge) intersection with theinner periphery of the rib 32. The rib 32 helps to provide a fuel-tightseal between the end of the collar, and the immediately adjacent surface30 representing the rim of the lockbolt aperture in the adjacent member16 as disclosed in U.S. Pat. No. 3,094,017. It is known that without thesealing ring a substantial percentage (e.g., on the order of 10 percent)of otherwise adequately clamped members, may permit leakage of fluidsdue to scratches or imperfections in either the end surface 33 or thecollar or the immediately adjacent surface 30 of the nearest memberbeing secured. Thus, the presence of rib 32 helps to insure the fluidtightness of the fit between the lockbolt and the secured members.

During swaging, when members 16 and 18 are initially compressed betweenthe head of the lockbolt and the collar 14, the annular ring 32 isdeformed immediately to fill in any cracks or imperfections in the twoadjacent surfaces 33 and 30 and any opening between member 16 andlockbolt 12. The preferred angle between the conic surface and the axisof the collar 14 depends upon the size of the collar, and will typicallyvary from 20 degrees to 80 degrees as the collar increases from 3/16inch diameter. Similarly, the external diameter of the rib 32 where itbegins to project from the end face 33 and its projecting length beyondthe end face 33 will depend upon the diameter of the lockbolt and thecollar. As an example, for a lockbolt having a diameter of 3/16 inch,the axial projection of the rib is preferably between 1/64 inch and 1/32inch. The function of and criteria for selecting the dimensions of thesealing ring 32 are the subject of U.S. Pat. No. 3,094,017 to Champouxet al, assigned to the same assignee as the present invention.

Between the cylindrical portion 26 and end face 33 the collar has anexternally tapered region 28. The dimensional criteria of the taperedregion 28 are determined generally by the amount of cavity space definedbetween the tapered exterior surface of the collar 14 and the internalwall of the swaging die 20 necessary to accommodate collar materialdisplaced during swaging so as to prevent the aforementioned reverseflow effect in accordance with this invention. Thus, the selection ofthe point longitudinally of the collar where the taper begins, the pointwhere the taper ends, and the angle or configuration of the taper aredetermined by the basic criteria that a spatial cavity must be providedwhich is sufficiently large to receive or pocket substantially all ofthe excess transitory material displaced in the direction of member 16during the swaging process.

If the spatial cavity is not large enough, the excess material fills upthe cavity and then flows radially inward of the lockbolt ultimatelyforcing longitudinal reverse material flow along the lockbolt away fromparts 16 and 18 so as to create the undesired tension in the lockboltwhich shrinks its diameter and loosens its fit in the parts 16 and 18.However, the location and configuration of the taper must not eliminateso much collar material as to create a deficiency precluding substantialfilling of all of the circumferential grooves between ribs 22 formed onthe lockbolt 12. If the taper begins too far from the collar endengaging member 16, not enough collar material will be present in thebody at the collar to sufficiently fill the grooves nearest member 16.

It is possible that the external taper of the collar may be given alongitudinally convex or concave form while meeting the above mentionedrequirements. For reasons of simplicity, minimum cost and effectiveresults, however, a straight taper is preferred, extending from betweenapproximately the longitudinal midpoint of the collar to the end face33. The taper angle relative to the longitudinal center line of thecollar is preferably on the order of 13 degrees, ±5 degrees, as shown inFIG. 1. Within this range, a spatial cavity is provided which permitssufficient volumetric expansion of the collar in the vicinity of the endof the collar adjacent the member 16 from the flow of excess collarmaterial, while still providing sufficient collar material to fill in atleast a substantial portion of each of the circumferential grooves oflockbolt 12 sufficient to securely lock the collar 14 to the lockbolt12.

The collar 14 is adapted to be swaged onto a lockbolt such as that shownin FIG. 2. The lockbolt shown specifically in FIG. 2 is of aconfiguration disclosed in application Ser. No. 400,334, entitled "WedgeHead Pin Fastener", by Louis Champoux, and assigned to the same assigneeas the present invention. Briefly, this lockbolt comprises successivelyin the longitudinal direction, a double angled head portion 36; acylindrical shank portion 38; a securing portion 40 having successivelyspaced annular ribs 22 formed by circumferential grooves, and aroundwhich the collar 14 is to be swaged; a breakneck portion 42; and agripping portion 44. The gripping portion permits the lockbolt to besecurely held during swaging, and the breakneck portion permits thegripping portion to be broken off after swaging is completed.

The sequence of the swaging process is shown in FIGS. 3-6. The collar 14is initially positioned over the securing portion 40 of the lockbolt 12.Members 16 and 18 are then pulled tightly together by the action of theswaging die 20 compressing them between collar 14 and the imbedded headportion 36 of lockbolt 12. The bore 48 of swaging die 20 has a flaredentrance 50 addressed to the collar 14. The bore 48 at the end 49 of die20 is larger than the diameter of the annular ring 23 of collar 14, andthus, side 23a of annular ring 23 at the one end of collar 14 will matewith the periphery of the bore 48 at some point along the flaredentrance 50. Behind the flared entrance 50, the bore 48 reduces to adiameter which is slightly less than the diameter of the cylindricalportion 26, so that as the swaging die is driven toward the plate member16, the collar 14 is gradually deformed along its longitudinal dimensionand molded to the ribs 22 of the securing portion 40 by the continuedadvancement of the swaging die 20.

A substantial amount of collar material is forced immediately inward ofthe collar, filling in around the annular rings 22 of the lockbolt inthe circumferential grooves thereof, with the excess collar materialbeing forced toward near member 16. As swaging proceeds, the amount ofexcess material being moved gradually decreases because of the presenceof taper portion 28. The spatial cavity created between the decreasingexterior diameter of the collar 14 in the tapered region 28 relative tothe flared entrance 50 of cavity 47 provides room for the accommodationof collar material which is being displaced toward plate 16. Aperipheral bulge 52 of collar material accumulates at the flaredentrance 50 to cavity 47 during swaging, which bulge gradually decreasesin volume as swaging proceeds because the increasing accommodation ofexcess collar material by tapered region 28.

When swaging has been completed, as shown in FIGS. 5 and 6, there willtypically be a slight peripheral bulge 53 in the vicinity of that end ofthe collar presented immediately adjacent member 16. Referringspecifically to FIG. 5, the tapered region 28 is configured relative tothe bore 48 of swaging die 20 such that at completion of swaging, withthe swaging die end 49 contacting surface 30 of member 16, there willremain a small volume of space 54 between surface 30, the flaredentrance 50 of swaging die 20, and the surface of the collar. Theprovision for such a volume of space insures that substantially alltransistory material has been accommodated by the spatial cavity. FIG. 6shows a lockbolt and collar combination after swaging has beencompleted, illustrating the peripheral bulge 53, and wherein thegripping portion 44 of the lockbolt has been preferably broken off atthe breakneck portion 42.

By thus providing a lockbolt collar with a tapered region extending fromsubstantially the longitudinal midpoint of the collar to the collar endadjacent the overlapped plate members, excess collar materialaccumulated during swaging flows continually in the direction of theplate members instead of proceeding radially inward toward the lockboltin the vicinity of plate members and then away from the plate memberslongitudinally of the lockbolt. The prevention of this reverse materialflow prevents the lockbolt from being elongated, and hence preserves theoriginal tight interference fit between the lockbolt and plate members.

Although an exemplary embodiment of the present invention has beendisclosed herein for purposes of illustration, it will be understoodthat various modifications, changes and substitutions may beincorporated in such embodiment without departing from the spirit of theinvention as defined by the claims which follow. For instance, it shouldbe understood that the end rib portion and opposite external annularring may take various configurations and may in some applications beeliminated. Furthermore, it should be understood that the configurationof the tapered region, although shown in the preferred embodiment as astraight taper proceeding from substantially the longitudinal midpointto one end of the collar, may take various other forms, as clarifiedabove. It is important, however, that the configuration of the taper besuch that a sufficient spatial cavity is provided for accommodation ofthe advancing excess material created incident to swaging.

What is claimed is:
 1. A lockbolt joint comprising:a workpiece having anaperture therethrough; a lockbolt having a shank extending through andfitting snugly in said aperture and having a portion projectingoutwardly beyond one surface of said workpiece; a lock collar swagedabout said portion and having a final peripheral bulge adjacent said onesurface, said final peripheral bulge having a converging portion whichconverges toward said one surface immediately adjacent said one surface,said final peripheral bulge being formed by swaging of a collar aboutsaid lockbolt with a swaging tool having an interior configuration whichinitially forces said collar into contact with said lockbolt and forms atransitory peripheral bulge of collar material at the end of said collarnot adjacent said workpiece, and which forces said transitory bulge tobe displaced progressively along the length of said collar as saidcollar is swaged into engagement with said lockbolt, the portion of saidswaging tool immediately adjacent said one surface being sized toaccommodate more than all said collar material therein upon engagementof said tool with said workpiece, thereby forming said final peripheralbulge, whereby longitudinal flow of said collar material in a directionaway from said workpiece is minimized, thus preventing excessive tensionon said lockbolt.
 2. The lockbolt joint defined in claim 1 in which saidportion has an annular lock rib spaced from said one surface, and saidlock collar is swaged into intimate contact with said lock rib, securingsaid lockbolt and said lock collar against relative movement withrespect to said workpiece.
 3. The lockbolt joint defined in claim 1,wherein said collar before being swaged about said lockbolt has agenerally ring-like shape and a central, generally straight axial borewhich permits said portion of the lockbolt to be passed therethrough,said collar having a radial thickness varying along its length,including a tapered region in which said radial thickness decreases inthe direction of said one surface, said tapered region being socontoured relative to said interior configuration of said swaging toolto accommodate said collar material therein when said tool engages saidone surface.
 4. The lockbolt joint defined in claim 3, wherein saidtapered region extends from substantially the longitudinal midpoint ofsaid collar to substantially the end thereof abutted to said one surfaceof said workpiece.
 5. The lockbolt joint defined in claim 4, whereinsaid tapered region forms a substantially uniform taper over its length.6. The lockbolt joint defined in claim 5, wherein said uniform taper issubstantially within the range of 8 degrees to 18 degrees.
 7. A methodof making a lockbolt joint wherein a swaging tool is used to swage alock collar onto an end portion of a lockbolt protruding through anaperture in a workpiece, comprising the steps of:fitting the shank ofsaid lockbolt snugly through said aperture in said workpiece so thatsaid end portion of said shank projects beyond one surface of saidworkpiece; placing said lock collar over said end portion of said shank,and; applying a swaging force with said swaging tool to said lockcollar, said swaging tool having an interior configuration whichinitially forms a transitory peripheral bulge of collar material uponbeing forced over said lock collar toward said workpiece, the portion ofsaid interior configuration closest to said workpiece being sufficientlylarge to accommodate more than all of said collar material containedtherein when said tool engages said workpiece, said force being appliedin the direction toward said workpiece until said swaging tool engagessaid one surface of said workpiece, said swaging tool thereby causingsaid transitory peripheral bulge to be initially formed at the end ofsaid lock collar spaced from said workpiece and to be displacedprogressively along the length of said lock collar towards said onesurface of said workpiece, said swaging tool upon engaging said onesurface of said workpiece thereby forming a final peripheral bulgehaving a converging portion which converges toward said one surfaceimmediately adjacent said one surface, longitudinal flow of said lockcollar material in a direction away from said workpiece thereby beingminimized and excessive longitudinal tension on said lockbolt therebybeing prevented.
 8. The method of claim 7 wherein said collar, prior tobeing swaged about said lockbolt, has a generally ring-like shape and acentral, generally straight axial bore which permits said portion of thelockbolt to be passed therethrough, said collar having a radialthickness varying along its length and including a tapered region inwhich said radial thickness decreases in the direction of the collaradjacent said one surface, said tapered region being so contouredrelative to said interior configuration of said swaging tool as toaccommodate said collar material therein when said tool engages said onesurface.
 9. The lockbolt joint defined in claim 8 wherein said taperedregion extends from substantially the longitudinal midpoint of saidcollar to substantially the end thereof abutted to said one surface ofsaid workpiece.
 10. The lockbolt joint defined in claim 9 wherein saidtapered region forms a substantially uniform taper over its length. 11.The lockbolt joint defined in claim 10 wherein said uniform taper has ataper angle relative to the longitudinal centerline of the collarsubstantially within the range of 8 degrees to 18 degrees.
 12. Alockbolt joint comprising:a workpiece having an aperture therethrough; alockbolt having a shank extending through and fitting snugly in saidaperture and having a portion projecting outwardly beyond one surface ofsaid workpiece; a lock collar swaged about said portion and having afinal peripheral bulge adjacent said one surface, said final peripheralbulge having a converging portion that converges toward said one surfaceimmediately adjacent said one surface, said peripheral bulge havingaccumulated collar material moved at least in part axially by a swagingdie during swaging, said swaging die being sized to accommodate saidcollar material therein without substantial axial flow of said collarmaterial away from said one surface when the forward end thereof engagessaid one surface at the end of a swaging stroke.
 13. The lockbolt jointof claim 12 wherein said lock collar prior to swaging has a generallyring-like shape and a central, generally straight axial bore whichpermits said portion of the lockbolt to be passed therethrough, saidcollar having a radial thickness varying along its length, including atapered region in which said radial thickness decreases in the directionof the collar adjacent said one surface.
 14. The lockbolt joint definedin claim 13 wherein said tapered region extends from substantially thelongitudinal midpoint of said collar to substantially the end thereofabutted to said one surface of said workpiece.
 15. The lockbolt jointdefined in claim 14 wherein said tapered region forms a substantiallyuniform taper over its length.
 16. The lockbolt joint defined in claim15 wherein said uniform taper has a taper angle relative to thelongitudinal centerline of the collar substantially within the range of8 degrees to 18 degrees.